1. Field of the Invention
This invention relates to drilling fluids commonly used in the drilling of earthen boreholes, especially for the exploration for and production of oil and gas. More particularly, this invention relates to a drilling fluid system which possesses desirable attributes regarding rate of penetration enhancement, lubrication, and clay inhibition, and further relates to a multi-component additive for drilling fluids, preferably pre-blended into a “single-container” additive for ease and efficiency in use, which specifically addresses rate of penetration, lubrication, and clay inhibition properties of the overall drilling fluid system.
2. Description of the Related Art
The present invention comprises a particular composition of water based drilling fluid (for fresh or salt water based systems) for use in the drilling of subterranean boreholes, commonly referred to as “wells.” The invention further comprises an additive for drilling fluids which comprises three primary components, directed toward improving the efficiency of the overall system.
The use of liquid drilling fluids, commonly known as “muds,” is well known in the art. In particular, this invention is directed toward drilling fluid systems used in the rotary drilling of wells, where a drill string is rotated, in turn rotating and applying weight to a drill bit, which drills through the downhole formation. Mud is pumped downhole through the drill string, through the drill bit, and circulated up the drill string/borehole annulus back to the surface.
Drilling fluids serve several fundamental functions: control of downhole formation pressures; removal of cuttings generated by the drill bit from the borehole; and cooling and lubricating of the drill bit. In addition to these fundamental functions of drilling fluids, drilling fluids preferably possess several desirable characteristics which can greatly enhance the efficiency of the drilling operation. Preferably, the drilling fluid exhibits rate of penetration enhancement characteristics, by having physical properties which “wet” the drill string and keep the cutting surfaces of the drill bit (whether of the roller cone or other configuration) clean. The “wetting” attribute is at least in part a function of the surface tension of the fluid. The drilling fluid also preferably has a high degree of lubricity, to minimize friction between the drill string and the wall of the borehole, an extremely valuable result being the minimizing of differential sticking (a situation in which the hydrostatic pressure of the drilling fluid column is sufficiently higher than the formation pressure, that the drill string is forced against the wall of the borehole and stuck). Yet another desirable characteristic is inhibition (that is, prevention from swelling) of formation solids (primarily clays and shales), which further reduces incidents of drill string sticking, undergauge holes, etc. Inhibition of clay swelling, in general, results from preventing the clays from adsorbing water.
The prior art has addressed, to some degree, these characteristics of drilling fluids in a piece meal fashion, with various products having been developed over the years which are directed toward (for example) one of the three desirable attributes. It can be readily appreciated that overall efficiency of the drilling fluid system is best achieved by incorporating all three of these attributes, into the system.
The present invention is a aqueous based drilling fluid system which comprises (in addition to the water phase, weighting material if any, and common components such as gelling materials) three primary additive components, of particular compositions and in preferred volumetric ratios of the three primary additive components one-to-the-other and within the overall drilling fluid system, which perform each of these desired functions (rate of penetration enhancement, lubrication, and clay inhibition). In addition, in a preferred embodiment, the invention comprises a drilling fluid additive in which the three primary components are “pre-blended” in a recommended ratio, one to the other, with the pre-blended additive thereafter added to a drilling fluid system to achieve a desired concentration of additive within the overall drilling fluid system.